The invention concerns a waveguide filter of the type that is inserted as a planar conducting structure in a cross-sectional plane of an elongated waveguide, perpendicular to the waveguide axis, between a feeding and an extending segment of the waveguide, and comprising at least one aperture configured for natural resonance for a selected transmission frequency.
Meeting the statutory regulations for the frequency band specifications, particularly with respect to the suppression of oscillator-generated interference radiation, e.g., a harmonic of the useful signal, represents a considerable share of the development costs for an equipment concept. At present, the use of waveguide resonators coupled to waveguide apertures as well as the use of resonance structures for FIN line circuits in the region of the fin-lines are known for waveguide circuits.
The layout of waveguide apertures is based on the known theories in waveguide aperture technology (Waveguide Handbook, N. Marcuwitz, Mc Graw-Hill Book Company, INC., Edition 1986). The waveguide apertures are formed as planar structures, for example with circular, slotted or H-shaped apertures and are inserted into a cross-sectional plane of an elongated waveguide, perpendicular to the waveguide axis, between a feeding and an extending segment of the waveguide. When used as band-pass filters, the apertures are operated with natural resonance, which for slotted apertures is set to an electrically effective slot length of one half the wavelength for the useful frequency, as is known. The transmission factor T of slotted apertures is determined by the slot width. Outside of their pass range, the waveguide apertures designed as band-pass filters have an attenuation course that corresponds only to the resonance curve. In particular, no concerted blocking of specific interference frequency multiples of the useful frequency is generally possible with these band-pass filters. For this, the known band-pass filters must be supported by additional filtering measures. In many cases, e.g. with small devices or with sensors, the volume required for the known band-pass filters causes interferece. The production costs for FIN conductors with resonance structures are relatively high.
A waveguide filter is furthermore disclosed in the EP 0 029 276 A1, which is composed of four planar conducting structures that cooperate in the waveguide field and which are integrated into the wall of a waveguide that is fed by a transmitter. The conducting structures are integrated across the circumference of the waveguide in a cross-sectional plane into the wall area, displaced by 90xc2x0 to each other, and respectively feed into an extending waveguide segment. In addition to a central aperture that is laid out for natural resonance for a transmission frequency, each of the conductive structures has two identically configured apertures, designed to suppress interference frequencies. These apertures are arranged on one longitudinal side of the central aperture, so that with respect to their longitudinal expansion, they are not positioned in the center of the symmetry axis for the conducting structure, which runs parallel to the field strength vectors.
It is the object of the invention to create a band-pass filter for waveguides, which simultaneously functions as a blocking filter for the targeted suppression of interference frequencies.
The above object is solved in accordance with a first aspect of the invention a waveguide filter that is inserted as a planar conducting structure in a cross-sectional plane of an elongated waveguide, perpendicular to the waveguide axis, between a feeding and an extending segment of the waveguide, that comprises a centrally arranged aperture formed for natural resonance for a selected transmission frequency f (ind 0), and that has, in addition to the centrally arranged aperture, two identically configured, parallel, spaced-apart apertures, and wherein: the identically configured apertures are formed for natural resonance for an interference frequency f (ind S1) to be blocked by the waveguide filter, and the apertures are arranged in the conducting structure such that, relative to a longitudinal expansion of the respective apertures, the apertures are positioned respectively in the center of a symmetry axis for the conducting structure, which axis runs parallel to the field strength vectors for the waveguide.
The above object is achieved according to a further aspect of the invention by a waveguide filter, that is inserted as a planar conducting structure in a cross-sectional plane of an elongated waveguide, perpendicular to the waveguide axis, between a feeding and an extending segment of the waveguide, and comprising at least one aperture configured for natural resonance for a selected transmission frequency f (ind 0), and wherein the conducting structure has a centrally arranged aperture configured for natural resonance for an interference frequency f (ind S1) to be blocked with the waveguide filter; and, in addition to the centrally arranged aperture, the conducting structure comprises two identically designed apertures, which are configured for natural resonance for a selected transmission frequency f (ind 0) and are arranged symmetrical to the central aperture. Modifications of the invention are described.
The advantage of this invention is that the transmission of a useful frequency and a targeted suppression of interference frequencies are possible with a single component and at low expenditure. The waveguide filter according to the invention makes it possible to adhere to production tolerances at a low cost and requires only a low installation depth. Owing to its symmetrical arrangement, the excitation of the interference mode is at a minimum.
Exemplary embodiments of the invention are explained in more detail with the aid of the drawing.